The proposed research is an extension of previous studies performed by this investigator on the growth and development of sympathetic ganglia in vivo. This work has defined (a) the developmental profiles of neurotransmitter enzymes, (b) the formation of synaptic connections during growth, (c) a bidirectional flow of regulatory information at the synapse during development, and (d) the nature of the trans-synaptic message regulating sympathetic neuron maturation in mouse superior cervical ganglion (SCG). The present studies will utilize this model system to investigate the genetics of neuronal maturation, with particular focus on the genetic basis of anterograde and retrograde trans-synaptic regulation. By applying the strain differences in neurotransmitter enzyme maturation, already defined by this investigator, to selective breeding experiments, we will study the interaction of (a) trans-synaptic control with (b) the information already encoded in the developing neuron. Characterization of transmitter enzymes physicochemically will determine whether strain differences are related to enzyme structure and will approach the problem of synaptic plasticity.